Process of producing a mixed crystal crop comprising mainly sodium bicarbonate and potassium pentaborate octohydrate



Patented Mnyl, 1945 UNITED STATES PATENT. OFFICE 1 2.314311' PROCESS OFPRODUCING A MIXED GRYST CEO? COMPRISING MAZNLY SODIUM BI- POTASSIUMPENTA- BORATE OGTOHYDBATE Frank Henderson lii'ay, Trona, Colli cssignorto American Potash & Chemical Corporation. 'lrona. 'Caliifi, acorporation of Delaware CARBONATE No Drawing.

c Claims.

This invention relates to a, process of producing a. mixed crystal.crop. consisting mainly of potassium pentaborate (KaBmOicJiHiO) andsodium bicarbonate (HaBICOo).

The process of the present invention produces a missed crystalwhicirupcn analysis. may conform exactly to the iormulae KzBmOzctI-hi)and humor. but under some conditions of operation. the saltsprecipitated do not coniorm exactly with said formulae. I reier.therefore. to

the product of the present process as a mixed Inthe process of presentinvention the mixed crystal crop is produced by a reaction betweenpotassium chloride (K61), borox (NlsBlOmlOHrO) and carbon dioxide Thesereagents react together in the presence of an aqueous solution inaccordance with the following equation:

From the foregoing' equation. it will be seen that potassium pentaboroteoctohydrote, sodium bicarbonate. and sodium chloride are all products oithe above reaction. such reaction may be can-led out to eiiectcrystallization from the solution of some pure potassium pentaborcte ochydrate. the sodium bicarbonate and sodium do formed remaining insolution. The present invention relates. however. to a process forcarrying out such reaction in order to crystallize both the potassiumpentaborste and I sodium bicarbonate formed. leaving sodium chlorideinrolution. Where the above reaction is carried out to crystallize onlypotassium pentaborste octohy'drste solution. the end liquors oi theprocess are high in potassium and'borote values. and such end liquorsmust be ordinarily processed to recover these values. where the processoi the present invention. however. is em- AND Application October 22.194;, Serial No. 501,300

values is high and the end liquor produced is low in the-valuable boronpotassium elements,

and consists mainly of a solution or sodium chloride. which solution maybe discarded.

The reaction between potassium chloride. horror. and carbon dioxide cannot. however. practically be carried out ln-the presence of water alonein such manner-cs to precipitate the larger part of thepotssdum andborstc values. Any atiomntt carry out the process in this manner resultsin formation oi so dense a. sludge that it can not be economicallyseparated from the. end liquor and a. pure prodnot produced. The processof the present invention is dependent up n adding potassium chloride,b'oraln and carbon dioxide to a liquor which to a. large extent mayconsist mainly at a solution or sodium chloride. The employment or sucha. solution of "sodium chloride as a, me-

dium for conducting the desired reaction permits the production of thedesired crystal crop without the formation oi sludzes cl such density asto inhibit practical separation or the crystals i'rom the end liquor ofthe process. The medium employed for conducting the reaction of thepresent invention maybe a. pure sodium chloride soltion. or may be partof the end liquor produced in the process of the present invention,since said end liquor is a liquor-high in sodium chloride and low inother constituents. The process 0! the present invention. however.dilfers from ordinary. yclic processes where an end liquor high invaluable constituents to.be recovered is returned.

The process oi the present invention will be more completely understoodfrom the followin: preferred examples of the process.

In the preferred example oi my process I employ the ,end liquor from a.previous operation. Such an end liquor is high in sodium chloride andlow in potassium and boron compounds. Once the cycle has beenestablished. there will always be available suflleient end liquor tomaintain the cycle. However, to start the cycle. itmay be desirable toprepare a substitute for the end liquor. A suitable substitute torliquor might be made merely by dissolving sodium chloride in water. Asomewhat better approximation oi the end liquor may be produced byadding a small amount or potassium chloride. For example, theprocess maybe started by employing as a substlfllje end liquor a solution formed byeddlng 29 .to..30 partsoi sodium chloride. and 3.3 parts or potassiumchloride to 100 parts or water.

ployed, the recovery oi the potash and boron The use of this syntheticliquor in place of on added all at the start of the operation. Likewise, the borax may be added all at the start of the operation if thecarbonating mechanism employed is capable of handling very heavy sludgesor suspensions. In other cases, it may be desirable to add the honor insteps during the carbonstion procedure. These ingredients should beadded in definite proportions. In order to form the desired crystalcrop, there should be added 3.08 parts of NuzBaOv (on the anhydrousbasis) for each part of KCl. There should also be added 3.5 parts of1:110 for each part of KCl, said added H to include the water ofcrystallization of the borne-which water is liberated during the courseor the reaction This added water is, or course, over and above the watercontained in the end liquor employed. In the carbonating operation 0.82part of carbon dioxide should be absorbed for each part or potassiumchloride added. These relative quantities should be maintainedessentially constant in the process independent of the amount or endliquor employed as compared with the other chemicals utilized The ratioof end liquor to other chemicals utilized may, however. undergo somewhatwide variations. Tins may be illustrated by comparing the amount or endliquor to be utilized with the potassium chloride added. The process maybe operated satisfactorily using as low as 8 and as high as 20 or morepounds of end liquor for each pound of potassium chloride added in theprocess. As a specific example of my process, I add 300 pounds orpotassium chloride to 2400 pounds of end liquor from a previous batch,the end liquor being obtained at C. This end liquor is suillcient todissolve all of the potassium chloride. but in the operation a smallresidue of other salts, including sodium chloride, may appear. Such aresidue might be filtered out before proceeding with the subsequentsteps. but for practical purposes may be allowed to remain.

To the solution or potassium chloride and end liquor I add 225 pounds orwater and i750 pounds of bore: (Na2B4O-IJOHzO). The borax contains about925 pounds or sodium tetraborate (NagBlO'I) and about 825 pounds ofwater of crystallization. Hence. the total water added to the end liquoris about 1050 pounds. In the car bonating operation about 240 to 250pounds of carbon dioxide is absorbed.

The progress of the carbonatinz reaction may be followed analyticallyand should be continued until the liquid phase or the product containsabout 29 parts or sodium chloride per 100 parts or excess water. It isto be understood that the and liquor from the carbonating operatlonis acomplex liquor containing sodium and potassium, chloride. bicarbonate,tetraborate, and. pentaborate compoimds. It is not feasible to analyzesuch a solution todetermine the actual amount of sodium chlorldepresent.In describing the ondliquorasonecontaininswpartaorsodiumchlorldepermopartsorexoesswatenlhave reference to the following systemof reporting the analysis at such solution:

mtnesystemenploaedallotthetloscontent otthecndliquorism bicarbonste. Allof the borate content of the solution is reported as made up or borax(NazBrOmlOI-BO) and potassium pentaborate (KiBloOmfiHzG). with theseassumptions made, it is then possible to state the relative quantitiesof chlorides which must be present as potassium chloride and sodiumchloride in the end liquor. The term "excess water" has reference to theamount or water present. which is not included in the born. the sodiumbicarbobate, and the potassium pentaborate octohydrate present.Obviously. the analysis of such an end liquor might be reported byvarious other somewhat arbitrary systems, in which the reported quantityor sodium chloride would, be different from that Indicated. Such wouldbe the case, for example, i! the bicarbonate content of the brine wasreported as potassium bicarbonate. instead or sodium bicarbonate. or ii'the tetraborate content was reported as notesslum tetraborate, orpartially as potassium tetraborate, in place or sodium tetraborate.

Obviously. another method of controlling the carbonation operation is toanalyze the sample oi the total'sluclge for its combined carbon dioxidecontent, in which case the'completion oi the reaction will be indicatedupon the absorption of the approxlmatelyflifl or 250 pounds of carbonidioxide to be used. I

In the carbonating step I prefer to employ a sutliciently ruggedcarbonator equipped with an agitator to permit agitating a relativelyheavy sludge. The partial pressure of carbon dioxide over the sludse inthe start of thereaction is about 150 mm. Hg. As the-reaction proceeds,the partial pressure increases and reaches about T600 mm. Hz. at 40' C.at the completion or the reaction. The carbonation should be carried outin a closed pressure vessel, using pressures or (carbon dioxideiii-excess or these minimum re- 40 qulrements.

18 required by the compound 8281010;

In this exampl or my process, I prefer to employ essentially pure carbondioxide .8115.

Upon the completion of the carbonatinc re-= action, the mixed crystalcrop is separated fromthe liquor by means, for example, or a centrifugalmachine. 'A portion of the liquor is removed from the cycle and theremainder saved for the next operation The centrifuge solids may bewashed, it desired. In washing operations, I prefor to use the coldsaturated solution of borex, instead of water. The washing fluid ispreferably kept apart from the bulk or the end liquor, and the watercontent 01. this wash fluid may replace the 225 pounds 01' water inwhole or in part, which were stated as added at the start or the cycle;The quantity 0! borax so entering the process with the wash liquidshould be subtracted from the amount of Iurther borax to be added.

To complete the cycle. I remove Item the cycle about 1050 pounds of endliquor which contains about 215 pounds or sodium chloride. The remainingend liquor (240d pounds) is returned to the next cycle. By the operationof this process, a mlsed'crystal crop, consisting essentially at about1500 pounds 01' sodium bicarbonate and potassium pentaboratcoctohydrate, is produced. Following the wasbinz operation on aliquortree basls, the product represents about 30% sodium bicarbonate.The remainder is pentaboratq'potassium, and combined water. Usually. Iflndfimewhat more pentaborate present than corresponds with the totalpotassium present. as However,

' 2,874,877 no solid phase of sodium chloride appears in the product Inexample oi my process, the ratio or suspended solids to total Sludge inthe finished batches is about 310%. This is quite thick or heavy sludge,and at times it may be desirable to operate with a sludge of lesserdensity. This may be accomplished by adding a greater amount of cyclicend liquor at the start of the operation,

As before stated, in place of the ratio oi end liquor to potassiumchloride of 8 to 1, ratios oi to 1 or more may be employed. The ratio ofthe other insrcdients added with the potassium chloride, however, shouldnot be essentially changed. Y

While the end liquor employed in the above example contained about 29parts oi sodium chloride per 100 parts by weight or excess water, it ispermissible to increase the sodium chloride concentrations up to aboutparts of sodium chloride per 100 parts of water.

Where, as in the above example, a part of the and liquor is discarded(1050 pounds), this represents a loss of about 13% of the potassiumvalues and about 6% oitbc boron values added. These losses are notexcessive, but maybe reduced by the following procedure: I have foundthat this end liquor is an unstable liquid, and, if the-end liquor beagitated for a period of several days-sometimes up to a week, asecondary crystallization occurs. In this secondary crystalllzationthere is crystallized a mixed crystal crop which contains predominantlythe ingredlents sodium, potassium, tetraborate, and pentaborate. Themixed crystal crop may be calcu lated in the main to NaeBaO-v andK213111010 (with some NaHCOi and NBcBxoOn), but microscopic and physicalchemical tests indicate that not all these compounds are the true solidphases present. The practical effect of the crystallization of thissecondary crop of mixed crystals, however, is the tact that thiscrystallization markedly reduces both potassium and borate contents ofthe and liquor.

In one example at the process or the present invention this secondaryprecipitation reduced the boron and potash values in the end liquor toonly 2% and 4% of the boron and potassium all added. This second crop ofcrystals may be used in various manners. For example, it may be added tothe original batch, when the potassium chloride, etc. are added. Underthe influence of CO: and oi the relatively high KCl concentrations, thissecond, mixed-crystal crop seems to become converted to about the samecomposition as the first crop, above described.

While in the foregoing example horas, l. e., the deco-hydrate of sodiumtetraborate was employcd, other hydrates of sodium tetraborate may beobviously employed, such as NaaBaOiSHrO, NaaBsOvAHaO; or calcinedproducts such as NasBsOrBBHrO, or even pyroborate (NazBsOr). Insubstituting these for ommon borax, the total quantity of water enteringthe reaction (excluslve or the water in the end liquor cycled) must bekept constant; that is, any water of crystalllzation oi the borax orsodium fetraborate employed, plus the added water, should always hearthe relationship of about 3.5- times 0! the added potassium chloride,while the anhydrous sodium tetralzlorate content should maintain therelationshlp of 8.08 to 1 KCL As an example of using a partiallycalcined borax as a raw material, I employ a product previouslydehydrated to a water content of about 25%, or to about 3.8 mols H(Naa'BeOaiEHhO) sufllcient 0! said raw material being taken to supplythe aforesaid 925 pounds or Nachos. To 725 pounds of water I add 800pounds of KC], most of which dissolved immediately. I set aside 2400pounds or end liquor from a previous batch. In this instance, I electedto add about 500 pounds of it to the aforesaid 725 pounds oi-water and300 pounds of K01. This resulted in the complete dissolution of the K01.In this experiment, I also elected to add the calcined boralx, and theremainder of the cyclic end liquor gradually and continually during thecarbonation. However. I took steps to assure that sulilcient calcinedborax was added, so that inspection of the sludge showed the presence ofcrystals or NMBiOIJOHIO until the com letion of the reaction. Over a.period oi. ten hours, 1 added said components, together with 245 poundsof carbon dioxide. Partial pressure of CO: at the start of thecarbonation was about mm. Hg.

Upon' completion of the carbonation, the batch was identical withthe'example described above, and the procedures followed from that pointwere the same. Yields. etc... were of course the same.

The-process is of value in recovering potasslum and/or boron values fromsolutions contaming the same, together with sodium chloride. Forexample, in the process of my copending application, Serial No. 507,299,filed October 22, 1948, for the production of pure K:BicOic.8H20. thereis produced an end liquor high in potassium and boron. This liquor maybe treated by the KCl Benz mo CO: Egg,

Ingredients a. a batch. in

present pieces 300 1.750 225 2&5 2400 Ingedients already added toteliquorgobcrotrcotedby this procus 80 I15 225 15 Dillerence, additionalingredb I taut:to lie adg l ed iloliquorto e rcpresca process. 210 1.615000 230 2.400

80, such a liquor, prepared according to the second line above. may bere-treated. and caused to yield a. valuable mixed crystal cropcontaining potassium pentaborate or the equivalent thereoi. whilerecovering valuable boron and potassium values therefrom. It must beremembered that the liquor to be re-treated had already produced a crop0! pure KcBmOmBHzO, and consequently that the mixed crystal cropproduced by addition of further (210 lb.) KCl. etc., will not be quitethe same as the mixed crystal crop produced trom the ingredients listedin the first column above. However, since the composition or the mixedcrystal crops obtained by the operation or the present process are knownto be somewhat variable and since despite such variations theyconstitute valuable and useful products, this variation is of littleconsequence.

In my copending applications Berlnl'lios. 460,-

278, fliedBeptember 80. 1942: 462,425, iiled'o'cto' bar 17. 1943;486,675 filed November 23, 1942, and 507.298, filed October 22. 1943, Ihave described cyclic processes for absorbing and recovering carbondioxide from cases containing the same. which involve the precipitation01' either potassium pentaborate octohydrate alone or admixed withsodium bicarbonate but in which processes then'iixdcropisredissolvedinthe cycle.

While the particular forms of the process herein described'are welladapted-to carry-out the objects of the present invention. it is to beunderstood that various modifications may he made,

and thisinventlon isoi the scope set'ior'tli in'the appended claims.

I claim:

1. A process of manufacturing-a mined crystal crop, which comprisesadding to a solution con taininz mainly sodium chloride the ingredientspotassium chloride, hora: and water and carbonation the resultingsludge. the ingredients added and thecarbon dioxide absorbed being inproportions suitable for forming petitahorate octohydrate and sodiumbicarbonate, crystallizing a mixed crystal crop consisting es sentlallyor such latter compounds during the carbonation operation whilecompleting the soluticn oi the inaredients'added, and thereafterseparating the mixed crystal crop from the 'pro duced mother liquor.

2. -A process of manufacturing a mixed crystal crop, which consistsessentially of potassium pentaborate .octohydrate and sodiumbicarbonate, which comprises adding potassium chloride, borax, and waterin essentially the proportions required to produce potassiumpentabor'ate octodrate and sodium bicarbonate to a solution containingmainly sodium chloride. and thereafter carbonating the resultingsludge-to oomplete the solution of the added ingredients whileprecipitating the mined crystal crop consisting essentially of saidpotassium pentaborate octohydrate and sodium bicarbonate'yandthereaitexi separating the crysml crop from the produced solution.

3. A process of manufacturing a crystal crop, consisting essentially ofpotassium pentahorate octo'hydrate and sodium bicarbonate, w'hlch conDrlses adding to a solution potassiumchlbrlde; bcrax, and water,carbonating the reshlnng; sludge, approximately 3.1 parts oiNazBio'l,3.5

parts oi H20, and 08 part of carbon dioxide beingadded for each part ofK01 added, the solution'to' which said inzredients are added beingemployed in the proportions at about 8 to 20 partsflior each part ofK0], said solution containing sodium chloride, precipitating said-mixedcrysthen' to! crop durlngfthejddition of carbon dioxide.andsepsratingtbemlxedcrystalcropn'omthe resulting solution.

.; 4. A process or manuiacturing a mixed crystal crop.consistinzessentiallyot potassium pentaborate OCtOlLVdfflfie 'and sodiumbicarbonate, which comprises adding potassium chloride, sodiumtetraborate, and water to a liquor containing mainly sodium chloride andcarbonating the 10 resulting-sludge, about 8.1 parts sodium tetraborate,3.5 parts Hi0, and 0.8 part or carbon dioxide and-8- to-m'l-parts'ofliquor being added for each part orscci addedi-precipitatinc the mixedcrysfil cropd urinai he carbonation operf5; ation while producingailiquor high in sodium chloride and low in raliieis'--oi r otassiurnand borata separatingtheiiduof iron the mixed crystel-crop, andrecycling-honorinthe first operalion.- i

qo 5. A'processiotmsnuiacturing a mixed crystalcropfconsistinkres'sentiafly of potassium pentaborate' octohydr'ete: andsodium bicarbonate.

,whl ch'--cohnpi 'lses;adding potassium chloride, so- "dium'tetrabbrate,and water to a liquor contain- 5 iiig mainly sodium chloride andcarbonating the resulting sludge. the potassium chloride, sodiumtetraborate, water. and carbon diorlde employed being in ratios suitablefor producing potassium pentabo'rate octoiiydrate and sodiumbicarbonate,

'30 precipitating said-mixed crystal crop din-in: the carbonationoperation while forming the residual solution, which consistsprincipally of sodium chloride and contains minor quantities only orpotassium and borate compounds, separating the 3:, mixed crystalcropirom said liquor. and using part of said liquor in said firstoperation.

6. A process oi manufacturing a mixed crystal crop, consistingessentially of potassium penta- 510 which comprises adding to a solutionconsisting mainly of sodium chloride, the ingredients potassiumchloride, borer, and water in proportions to form potassium pentaborateoctohydrate and sodium bicarbonate on carbonation. carbonating theresulting sludge to form and precipitate said ,ihi ted crystal cropwhileiorming a solution containing mainly sodium chloride and minorquantitles only or potassium and borate value. separating the mixedcrystal crop tron: said solution, so and thereafter subjecting theseparated solution to a secondary crystallisation operation to form asecond crystal crop which analyses mainly sodium tetraborate andpotassium pentaborate, thercbyfurther reducing the potassium and heretovalues of the liquor.

FRANK Enumson MAY.

borate otohydrate and sodium bicarbonate,

